The invention is directed to a process for the production of pure 4,4'-isopropylidene-bis(2,6-dibromophenol) by reaction of 4,4'-isopropylidene diphenol with a brominating agent in the presence of water and an inert organic liquid. 4,4'-isopropylidene-bis(2,6-dibromophenol) is employed as a flameproofing agent. For example, it is admixed with synthetic resins for this purpose. In order that the synthetic resin is not colored in an undesirable way, it is necessary to use a correspondingly pure, non-coloring 4,4'-isopropylidene-bis (2,6-dibromophenol).
It is known to produce 4,4'-isopropylidene-bis(2,6-dibromophenol) by brominating 4,4'-isopropylidene diphenol. As the brominating agent there is used bromine. The reaction is carried out in the presence of two liquid phases, namely, water and an organic liquid which is only slightly miscible with water. The 4,4'-isopropylidene-bis(2,6-dibromophenol) formed is recovered from the reaction mixture by filtration. The mother liquor resulting as the filtrate and which contains hydrogen bromide is used as the reaction medium for a subsequent charge (Jenkner, German Pat. No. 1,768,444).
It is also known to carry out the bromination with the addition of an oxidizing agent. As the oxidizing agent, there is primarily employed chlorine, alkali chlorate or alkali bromate, see Asadorian U.S. Pat. No. 3,546,302 or hydrogen peroxide, see German Offenlegungsschrift No. 2,227,439 and related Janzon U.S. Pat. No. 3,929,907. The entire disclosures of the Asadorian and Janzon U.S. patents are hereby incorporated by reference and relied upon.
A disadvantage of the known processes is that discoloring byproducts are formed to a considerable extent. The 4,4'-isopropylidene-bis(2,6-dibromophenol) separating from the reaction mixture contains this type of impurities in undesired amounts. Particularly if the motor liquor is reused as the reaction medium the 4,4'-isopropylidene-bis (2,6-dibromophenol) is obtained in highly impure form. Of course, it is possible to purify the material from discolouring byproducts, but thereby the yield is reduced considerably.